-have a water vascular system which helps them move around in the water

-have gills

-reproduce sexually or asexually

Digestion

-sea stars are carnviorous, their stomach folds out to digest the food then folds back
in.

-sea cucumbers and brittle stars eat small organisms

-sea urchins are herbivorous

Their nervous system has a central nervous ring with nerves that go down each arm. There are
touch receptors and eyespots on each arm. They have radial symmetry but the larvi are bilateral. The exception are sea cumcumbers
which have bilateral symmetry even as an adult.